Television antenna having adjustable tuning network



April 12, 1960 E. G. HILLS ET AL 2,932,822

TELEVISION ANTENNA HAVING ADJUSTABLE TUNING NETWORK Filed Oct. 25, 1954 :5 Sheets-Sheet 1 VENTORS Elmerzgffills April 1960 E. G. HILLS ETAL 2,932,822

TELEVISION ANTENNA HAVING ADJUSTABLE TUNING NETWORK Filed Oct. 25, 1954 3 Sheets-Sheet 2 INVENTORS Elmer G11 Hills United States Patent TELEVISIGN ANTENNA HAVING TUNING NETWQRK Elmer Guy Hills, Des Plaines, and Julius Chicago, Ill.

ADJUSTABLE Tunitl,

The present invention relates to television antennas, and more particularly to indoor television antennas for the reception of signals in the low, high and ultra high frequency television bands.

It is well recognized that present indoor television antennas when adjusted for reception in the low frequency television band (54-88 megacycles) are subject to two major criticisms. They are either too large and awkward for home use, or else they present a serious impedance mismatch to the transmission line, causing an attenuation and, hence, loss of the received signal. A few antennas small in physical size have been produced to provide a good impedance match to a transmission line by including therein an adjustable impedance matching network. However, in such case the operator must make an appropriate impedance matching adjustment for each particular station desired. Users of such indoor television anteuna are thereby exposed to a bothersome and annoying manual operation of tuning the antenna for each change of station. Likewise, this impedance matching adjustment usually requires a complicated switch which increases the initial expense and subsequent maintenance costs of the antenna.

An additional disadvantage of the present indoor television antennas resides in that they either operate only in the ultra high frequency television band (470490 megacycles), or they cover the low frequency television band (5488 megacycles) plus the high frequency television band (l74216 megacycles) without either a good gain or a good impedance match in the ultra high frequency television band. Therefore, it would be desirable to provide an indoor television antenna which would be of relatively small size, which would eliminate the necessity of antenna adjustment when changing from one station to another, and which would provide a good gain and a good impedance match to the transmission line for all reception desired at a particular location. In many locations the television set owner can get one channel at most, such as one of channels 2 to 6 in the low or .88 megacycle band, one or more channels such as channels 7 to 13 in the 174-2l6 megacycle band, and several in the 470-890 megacycle band. It would be desirable to provide an antenna providing a perfect impedance match for one station in the low frequency band, and excellent matches for stations in the other two bands.

Accordingly, it is an object of the present invention to provide an improved indoor television antenna having the desirable characteristics noted above.

it is another object of the present invention to pro vide an indoor antenna which produces an almost perfect impedance match to one station in the low frequency television band, and which produces excellent impedance matches to all stations in the high and ultra high frequency elevision bands while eliminating the necessity of antenna adjustment when changing from one station to another.

It, is still another object of the present invention to provide an indoor television antenna which has a considerably narrower beam width and resultingly higher gain than a conventional half wave length dipole in the ultra hivh frequency television band, and which simultaneously provides good impedance matches to stations in the low, high and ultra high frequency television hands.

it is a further object of the present invention to provide an impedance matching network for an indoor television antenna which is adapted to produce an excellent impedance match for any selected station in the low fre quency television band and a good impedance match for all stations in the high and ultra high frequency television bands, and wherein said selected station may readily be changed if desired.

It is a Still further object of the present invention to provide an impedance matching network for an indoor television antenna which will provide a fair impedance match to a transmission line for all frequencies in the low frequency television band and which will produce a compromise antenna performance in the low frequency television band while providing excellent antenna performance in the high and ultra high frequency television bands.

Still another object of the invention resides in the provision of an improved strain relief device for television antennas.

Another object of the present invenL'on resides in adapting a pair of hollow conducting tubes to serve both as a parallel conductor transmission line and as a short mast or upright support for said antenna.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed plication.

For a better understanding of the present invention reference may be had to the accompanying drawings in which:

Fig. 1 is a front elevational view of an indoor television antenna embodying the present invention;

Fig. 2 is a right side elevational view of a television antenna embodying the present invention, with the right element of the dipole removed;

Fig. 3 is a plan view of the indoor television antenna of Fig. 1;

Fig. 4 is a fragmentary enlarged sectional view taken substantially along line #4 of Fig. 1;

Fig. 5 is a sectional view taken along line 5-5 of Fig. 4, assuming that Fig. 4 shows the complete structure;

Fig. 6 is a sectional view taken on line 6-6 of Fig. 5, assuming that Fig. 5 shows the complete structure;

Fig. 7 is an enlarged longitudinal sectional view of a removable cartridge comprising one component of the antenna of the present invention taken substantially at line 77 of Fig. 4;

Fig. 8 is a bottom plan view of the base of the antenna of Fig. 1 with the rubber supporting feet removed;

Fig. 9 is a fragmentary sectional view taken along line 9-? of Fig. 8 showing the rubber feet in place;

Fig. 10 is an enlarged fragmentary perspective view of a portion of the antenna of Fig. 1;

Fig. 11 is a schematic circuit diagram of the antenna of the present invention;

Figs. 12, i3, 14 and 15 are curve diagrams to aid in understanding the present invention; and

Fig. 16 is a schematic diagram of an alternative component for use in the antenna of Fig. 1.

Briefly, the present invention comprises an indoor television antenna of the dipole type adapted for reception to and forming a part of this apin the low 54-88 megacycle), high (174-216 megacycle) and ultra high (47 -890 megacycle) frequency television bands, which may be readily mounted on or near a television receiver, and which is somewhat decorative in nature. Each half of the dipole is approximately equal to an equivalent wave length in the center of the ultra high frequency band, slightly longer than the equivalent quarter wave length in the upper portion of the high frequency television band, and considerably shorter than the equivalent quarter wave length in the low frequency television band. An impedance matching network is adapted to provide the dipole elements with a substantially consistent output impedance of the order of 300 ohms throughout the low, high and ultra high television frequency band. This network will effectively match the characteristic impedance of conventional transmission lines used with television receivers. This network, for convenience is comprised of electrical component cartridges which may be manually removed from and inserted into appropriate sockets provided therefor. Cartridges of predetermined electrical components in predetermined' relationship may be inserted in the impedance matching network to alter the reception characteristic of the antenna. These readily removable and replaceable cartridges of the impedance matching network may be arranged so that an almost perfect impedance match results to one station in the low frequency television band and excellent matches result to all stations in the high and ultra high frequency television band. The same arrangement of different removable cartridges of the impedance matching network will produce a good impedance match to all stations, including compromise antenna performance within the low frequency television band and good impedance matches to all stations in the high and ultra high frequency television bands. But regardless of whether the antenna is preadjusted for reception of only one or all stations within the low frequency television band, the antenna is characterized by providing a considerably narrower beam width and resultingly higher gain than a half wave length dipole in the ultra high frequency television band while still offering good impedance matches in the low and high frequency bands. The antenna also includes improved strain relief means.

' any conducting objects resting Referring now to the drawings, there is illustrated in Figs. 1 through 3 the assembled indoor television antenna of the present invention, generally indicated at 10. As illustrated, the visible components of said assembled antenna 10 comprise a molded circular base 11, a pair of parallel support tubes 12 extending upwardly from said base, a dipole support 13 mounted on of said tubes, a dipole 14 specifically comprising dipole elements 14a and 14b suitably secured to the support 13, and a transmission line 15 connected to the dipole. The base 11 is adapted to provide a foundation for the antenna 10, and, in particular, to support the pair of parallel tubes 12. To provide stability and cushioning means for said base 11, which is commonly disposed on top of an associated television receiver, there are provided rubber feet or buttons 16, as best illustrated in Figs. 8 and 9 of the drawings, which tend to protect the surface of the television set and to greatly increase the friction between the base 11 and the top of said television set. These feet 16 may be inserted in suitable openings 17 molded in the base 11. While the base 11 is illustrated as having a circular shape, it will be understood that the base may embody any configuration. It is, however, preferable that the base 11 be manufactured of molded insulating material such as polystyrene or the like. In order to provide support and stability for the pair of parallel tubes 12, the central or middle portion of said base 11 is elevated and provided with a pair of spaced cylindrical cavities defined therein during the molding'operation. The supports 12 are insertable into these cavities.

For the purpose of providing a strain relief device for the parallel wire transmission line 15, there is integrally the upper ends molded with the base 11 a stud 20 which may be inserted through an opening provided in the insulating material of polyethylene or the like of said transmission line 15. The stud 211 may then be heated by a soldering iron or other hot device to cause the stud 20 to melt or flow, so that a head2tla is formed on the end thereof, as illustrated in Fig. 9 of the drawings. The stud 20 with its enlarged head secures inposition said transmission line 15 to said base 11 and relieves the electrical terminals 15a and 151) connected to the conductors forming a part of the transmission line 15 of any mechanical stress.

To secure bot the pair of hollow tubes 12 and the transmission line terminals 15a and 15b to said base 11 and to provide an electrical connection between said transmission line 15 and said pair of hollow tubes 12, which serve both as conductors and supports, a pair of screws 21 or like fasteners are employed. These screws 21 enter openings in the base 11 aligned with the cavities receiving the tubes 12, and threadedly engage the lower ends of the tubes 12, thus firmly securing the tubes to the base 11 and electrically connecting the transmission line 15 thereto. With this arrangement the tubes 12 provide a parallel conductor transmission line and a short mast for the antenna 18. The diameters and relative position of said hollow tubes 12 are such as to produce a transmission line with the same characteristic impedance as the parallel wire transmission line 15.

In accordance with the present invention, the pair of parallel tubes 12 are somewhat L-shaped, with the upper ends disposed in a horizontal plane to extend into the dipole support 13 mentioned above. The length of said hollow tubes 12 between the base 11 and the dipole support 13, and, accordingly, the height of said antenna 10 is such as to provide a pleasing appearance for the antenna it when resting on a television set. The dipole structure mounted on the upper ends of the tubular conductors 12 is sufficiently high above the base 11 so that upon the same support do not substantially reduce the field of region of the dipole elements 14a as the base 11 the signal in the and 14b.

In order to provide a support for the dipole elements 14a and 14b, and to provide a housing for a suitable impedance matching network, the dipole support 13 comprises an insulating plate 22 formed of polystyrene or the like. To secure the insulating plate 22 of the dipole support 13 to the top horizontally disposed ends of said pair of parallel tubes 12, the plate 22 includes a pair of integral hollow cylindrical appendages'22a into which the top horizontal ends of said pair of parallel tubes 12 may be inserted. The longitudinal axes of the appendages 22a are generally perpendicular to the plate 22 integral therewith, whereby the plate 22 is disposed in a vertical plane, as illustrated in the drawings. The plate 22 is secured to said tubes 12 by means of screws 23 extending through appendages 22a and threadedly engaging tapped openings in the portions of tubular conductors 12 extending into the openings defined in appendages. 22a.

For the purpose of supporting the dipole elements 14a and 14b from the insulating plate 22, there are provided a pair of brackets 25 and 26. Looking at the antenna from the front as viewed in Fig. l of the drawings, the bracket 25 is the right-hand bracket, and the bracket 26 is the left-hand bracket. These brackets comprise a portion 25a and 26a, respectively, extending parallel with the plate 22 and secured to the plate on the side thereof from which the appendages 22a project by rivets 27 and 28 extending through the brackets 25 and 26 and the plate 22. The rivets 27 secure the upper ends of the portions 25a and 26a of the brackets 25 and 26, while the rivets 28 secure the lower ends of these bracket portions 25a and 26a to the plate 22. As may be observed from Fig. 5 of the drawings, these brackets. are secured adjacent the 22 so that angularly projecting an integral part of the associated brackets 2:7 and 26, respectively, are disposed to project beyond each side of the supporting plate 22. Preferably the cars 25?: and 25b which extend toward the rear of the antenna as viewed in Fig. 1 of the drawings are disposed at such an angle that if they were extended they would intersect substantially at a right angle. These ears 25b and 2622 provide very simple support means for the dipole elements Side" and 1412. As best shown in Figs. 4 and of the drawings, each of the ears 25b and 26b is provided with a notch 29 to facilitate securing the dipole elements thereto.

In accordance with the present invention, the dipoles 14a and 1411 are identical and each comprises a conducting rod 39, formed of aluminum or the like, bent to form a sort of U-shaped element, with the bight of the U of arcuate shape, and the arms of the U converging thereby to form a sort of pie-shaped member or wing. Preferably the converging arms make an angle of the order of The arms of the U are secured to a suitable conducting bracket 31 which preferably comprises twin stampings 31a and 31b secured together by suitable rivets 32, and including suitably formed depressions for clampingly receiving therein the ends of the rod 36 defining the dipole elements i i-a and 141;, respectively, as best shown in Fig. 10 or" the drawings. Each stamping 31a and 31b of the bracket 31 is furthermore deformed to provide a rectangular recess 32 between the two stampings to receive therein one of the ears 25b or 2611, as the case may be. A suitable screw 33 extending through aligned openings in the bracket 31a is adapted to clamp the bracket 31 to the associated ear 25b or 2612. With this construction it will be apparent that assembly is very simple, since the screw 33 may remain in the openings defined in the bracket 31, and the ear 25b or 2612 may be inserted with the notch 2? receiving the screw 33, as clearly indicated in Fig. 10 of the drawings. By merely clamping the screw 33, the dipole element is then rigidly supported from the associated ear 25b or 26b, as the case may be, and is likewise electrically connected thereto and, hence, to the associated bracket such as 25 or 26. The rod 3b and associated bracket 31 comprise the entire dipole element such as Me or 14b. For decorative purposes only, it may be desired to include suitable additional means such as the coil member 36, which has one end hooked into the bracket 31, as indicated, and the other end connected to the bight of the dipole 36 by a suitable insulating member 37 so as not to interfere with operation of the dipole.

From the description included above it is apparent that the transmission line 15 is efiectively extended by means of the tubular conductors 12 to the supporting plate 22. The dipole elements 14a and 14b are similarly electrically connected to brackets 25 and 26, also supported from the plate 22. Thus far no electrical con nection has been provided between the tubular conductors l2 and the dipole elements 14a and 1415. To enable the antenna lii to operate satisfactorily throughout all three presently available television bands designated as the low, high and ultra high frequency television bands, and to permit selective control of the reception provided by the antenna, there are provided means for connecting the dipole elements 14a and 14b to the tubular conductors 112. This means comprises a a matching network including interchangeable capacitive and inductive elements arranged in the form of readily removable and replaceable cartridges. The electrical circuit can best be understood by first referring to Fig. 11 of the drawings. As there illustrated, the matching network comprises three cartridges schematically illustrated and generally designated as 33, 39 and 4d, respectively. These cartridges are structurally shown in other views of the drawings and there designated by the same reference'numerals.

side edges of the plate ears 25b and 26b, each They are, moreover, described in detail hereinafter. As is obvious from Fig. 11 of the drawings, each cartridge comprises a network including a capacitance and inductance in parallel. As illustrated, cartridge or network 38 comprises an inductance, 38a and a capacitance 38b connected in parallel, cartridge or network 3 comprises an inductance 39a and a capacitance 39b connected in parallel, and cartridge or network 40 comprises an inductance idd and a capacitance dill: shunted across a part of said inductance 49a. The cartridges or networks 33 and 39 may be considered series cartridges, since they serially interconnect an associated dipole with the transmission line 15. Thus, cartridge 38 connects dipole 14b to one of the tubular conductors 12, while cartridge 39 connects the other dipole 14a to the other tubular conductor 12. The cartridge 46 is a shunt cartridge or network and is connected across the junction. of the series cartridges 38 and 39, with the transmission line connected to the antenna and specifically across the tubular conductors 12. The cartridges 38 and 39 for any particular setup will be identical. Preferably there is also provided a small capacitor 41 connected across the adjacent ends of the dipoles 14a and 14b to correct the impedance of the impedance matching network comprising cartridges 38, 39 and 40 in the ultra high frequency band for slight mismatches caused by the distributed inductances and capacitances of the cartridges 38, 39 and 40.

Referring now to Figs. 4 to 7 of the drawings illustrating the structural arrangement for producing the circuitry of Fig. 11, the brackets 25 and 26 are electrically connected at their lower ,ends to a pair of U-shaped spring clips 42, specifically designated as 42a and 42!), respectively, only the clip 42:: being visible in the drawings. Preferably. the spring clips 42a and 425 are secured to the support 22 by the rivets 28, which also secure the lower ends of the brackets 25 and 26 to this support. As illustrated, the plate 22 includes a plurality of integral thickened portions 22b arranged in a predetermined spaced relationship, two of which are disposed so that the rivets 28 extend therethrough to clamp the spring clips 42a and 42b against these raised portions, whereby the spring clips, generally of U-shaped configuration, are disposed on the opposite side of the plate 22 from the brackets 25 and 26. Identical spring clips 43:: and 43b are secured directly above the spring clips 42a and 4%, respectively, on the other thickened portions 22b of the plate 22 so as to be capable of receiving and retaining the cartridges 33 and 39, which are preferably constructed The spring clips 43a and 43b are secured by rivets 44 which also extend through the raised integral portions 22b of the plate 22. In accordance with the present invention, the spring clips 43a and 43b are each connected by a suitable conductor 45 with the tubular conductors 12. As illustrated, one end of each conductor 45 is connected by the associated rivet 44 with the associated one of the spring clips 43a and 43b. The other end of each conductor 45 is connected in any suitable manner with the associated one of the tubular conductors 12. As illustrated, the conductors 45 extend generally parallel with the appendages 22a, and the fastening means 23 for me chanically securing the plate 22 to the tubular conductors 12 also electrically interconnects the tubular conductors 12 and the conductors 45.

To complete the electrical circuit, the spring clips, specifically designated as 42a and 43a, are interconnected by the removable cartridge 38, while the spring clips 42b and 43b are interconnected by the removable cartridge 39. As was mentioned above, these removable cartridges '38 and 39 may be identical, and the removable cartridge 38 is disclosed in detail in Fig. 7 of the drawings. As there illustrated, it comprises a hollow cylinder 47 of insulating material, such as fiber or the like, which cylinder is closed by suitable end terminals 48 and 49. These end terminals are interconnected within the housing 47 by means of the inductance 68a paralleled by the capacitance 38b, already discussed above. With the series cartridges 38 and 39 inserted in the associated spring clips 42 and 43, it will be appreciated that each dipole is electrically connected to its associated terminal 15a or 1511 through a parallel arranged inductance and capacitance.

To accommodate the. shunt cartridge 40, which may, except for the electrical characteristics, be very similar to the series cartridges 38 and 39, suitable spring clips 51 and 52 are secured to the conductors 45 so that the cartridge 40 is disposed generally perpendicular with the cartridges 38 and 39, and electrically connected across the conductors 45 and, hence, across the tubular conductors 12. To prevent getting'a shunt cartridge in the place of the series cartridge, or vice versa, the series cartridges 38 and 39 are of a different size from the shunt cartridge 40. Thus, such improper insertion of cartridges can never occur.

To provide the small capacitor 41 between the dipoles, there may be provided a suitable U-shaped conductor 41a having its bight portion secured as by rivets 53 to the supporting plate 22 and the arms of the U disposed adjacent the spring clips 42a and 42b, but spaced therefrom to provide the suitable electrical capacitance schematically designated as 41 in Fig. 11 of the drawings.

In order to improve the appearance of the antenna, the dipole support 13 preferably includes a suitable housing enclosing the plate 22 and associated cartridges 3%, '39 and 40. To this end there is provided a two-part insulated housing 55 comprising housing sections 55a and 55b. The housing section 55b is provided with a pair of openings to receive the tubular conductors 12. To secure the housing sections together, preferably the housing section 55b is provided with a threaded protuberance 56 (Fig. 6 of the drawings) for receiving a screw 57 extending through aligned openings in housing section 55a and plate 22. The two housing sections 55a and 5512 may have interfitting portions to provide a completely closed housing when the screw 57 is effective to clamp the two sections together.

The vertical portions of the tubular conductors 12 of the antenna 10 are located substantially at the center of gravity of the antenna, so that it is well-balanced on the base 11 with the dipole elements 14a and 14b in position. Because of the positions of the ears 25b and 2612, the Winglike patterns of the dipole elements 14a and 14b lie substantially in vertical planes and intersect each other at an angle of substantially 90. Thus, the dipole is adapted to receive horizontally polarized waves with the angle of maximum reception along the bisector of the approximate 90 angle or along the arrow A in Fig. 3 of the drawings, and with a narrow beam Width over the entire ultra high frequency band of approximately 2:1 frequency ratio. By having the upper and lower edges of each dipole element 14a and 14b make an angle of the order of 15 with each other, a fairly constant resistive impedance of the order of 300 ohms is obtained over the entire ultra high frequency band (470-890 megacycles). The dipole elements are preferably of the order of fifteen inches in length from the tip of bracket 31 to the bight of the U-shaped rod 30, since this is about the maximum size that would appear well on top of a television set in the average home location. With this size each dipole element is of the order of one wave length in the middle of the ultra high frequency band. Each wing of the above-described dipole 14a or 14b has an equivalent straight length of slightly longer than a quarter wave length in the upper portion of the high frequency television band, and, therefore, is inductive in impedance throughout the high frequency television band. On the other hand, each has an equivalent straight length considerably shorter than a quarter wave length in the low frequency television band, and, therefore, is capacitive in impedance throughout thelow frequency tele: vision band.

It is well known in the art that any antenna may be matched substantially perfectly to any transmission line impedance at any one frequency. However, as the attempt is made to receive signals at frequencies which deviate from the particular frequency for which it is matched, the matching of the antenna to the transmission line becomes progressively less effective. The rapidity with which the mismatch increases as the frequency deviates from that of the best match is a function of the volume of space occupied by the antenna in terms of the cubic wave lengths. This remains true regardless of the circuitry used in the impedance matching network. For this reason it is, therefore, possible with theantenna 10 of the present invention to obtain an excellent impedance match (that is, with a voltage standing wave ratio under 2 to 1). This can be obtained over substantially the entire ultra high frequency television band with a frequency ratio of 1.9 to l, and at the same time over substantially the entire high frequency television band with a frequency ratio of 1.24 to 1, and simultaneously over at least a small portion of the low frequency band with a frequency ratio of 1.62 to 1. Since there are definite limitations as to the size of an indoor television antenna, the antenna of the present invention is considered to be optimum size which may be attractively placed on the television set in the living room of an average home. With this limitation it is nevertheless possible for the present antenna 1% to be preadjusted to receive signals from all television stations within the high and ultra high frequency television band, and at least one television station in the low frequency television band. Since in most areas of the United States one can receive signals from only one television station in the low frequency television band, the antenna of the present invention would be entirely adequate if it were preadjusted for the one station in the low frequency television band either at the factory or at the retail outlet. This preadjustment will eliminate the necessity of repeated antenna adjustment after each change of station.

In order to conveniently preadjust the antenna '10 of the present invention for nearly perfect reception of one particular television station in a low frequency television band, the removable series cartridges 38 and 39 are provided with predetermined values of inductance and capacitance. The electrical characteristics of the shunt cartridge 40 will be the same for all channels within the low frequency television band. Thus, by selecting the proper series cartridges 38 and 39 to correspond with the particular station desired in a low frequency television band, a perfect match for this channel is provided. In short, series cartridges 38 and 39 adapted for reception of signals in any one of the channels 1 through 6 are installed in the antenna network to be used in those cities or regions in which only one television station transmits in the low frequency television band.

The characteristics of the antenna 10 can better be understood by reference to the curve diagrams of Figs. 12 to 15 of the drawings. Fig. 12 illustrates the reactance characteristic of the shunt cartridge 40 with the abscissae representing frequency in megacycles, and the ordinates indicating reactance, either capacitive or inductive. The curve B, which becomes infinite at about the top end of the high frequency television band, shows that the reactance is a zero reactance both at zero frequency and somewhere between the high and ultra high frequency television bands. It is noted that the reactance of the shunt cartridge 40 is inductive in all three television bands, but being exceptionally inductive in reactance at the top end of the high frequency television band.

Fig. 13 illustrates the reactance characteristic of the series cartridges 38 and 39. Curve C, which is a discontinuous reactance curve becoming infinite at a frequency between the low frequency and the high frequency telel for the particular vision bands, also becomes zero at zero frequency. This reactance as shown by curve C is inductive in the low frequency television band, but capacitive in the high frequency and ultra high frequency television bands. The series cartridges are adapted to produce near perfect reception of any particular channel in the low frequency television hand. For different channels in this low frequency band, the series cartridges 38 and 39 present diiferent inductances, which is the predominant reactance element in the low frequency band, but the capacitances are the same, so that they effectively become identical in reactance in the high and ultra high frequency bands where the capacitance of the cartridges becomes dominant. The schematic diagram of the antenna as heretofore described and illustrated by Fig. 11 of the drawings indicates the circuit arrangement for the shunt and series cartridges. It should be understood that other circuit arrangements producing the reactance characteristic of Figs. 12 and 13 may be used instead of the cartridges described.

It will likewise be understood that the output impedance of the antenna 10 at the terminals 15a and 15b is equivalent to the resultant impedance obtained by comining the impedance of the parallel tube transmission line comprising tubular conductors 12, with the impedance of the matching network comprising cartridges 38, 39 and 40 and the impedance of the dipole elements 14a and 14b. This resultant impedance remains at a substantially constant resistive impedance of approximately 300 ohms frequency corresponding to the single television station in the low frequency band and for all frequencies throughout the high and ultra high frequency television bands. In the low frequency television band, the reactance of the dipole is capacitive, that of the series cartridges 38 and 39 is inductive, that of the shunt cartridge 44) is inductive, that by virtue of capacitor 41 is capacitive, and that of the tubular conductors 12 is resistive, which when combined by virtue of the circuitry of Fig. 11 produces the desired approximate 300 ohm resistance. In the high frequency television band, the reactance of the dipole is inductive, that of the series cartridges 38 and 39 is capacitive, that of the shunt cartridge is inductive, that of the capacitor 41 is obviously capacitive, and that of the tubular conductors 12 is resistive, which when combined produces an approximate resistance of 300 ohms. In the ultra high frequency television band, the reactance of the dipole is substantially zero, and its impedance is resistive and approximately 300 ohms, the reactance of the series cartridges 38 and 39 is capacitive, but low in value, that of the shunt cartridge 40 is inductive, and that of the capacitor 41 is obviously capacitive, while that of tubular conductors 12 is zero, which when combined produces an equivalent resistive impedance of approximately 300 ohms.

It will be appreciated that there are areas in which two stations transmit within the low frequency television band. In such case it may be desirable to obtain a compromise impedance match for compromise performance of the antenna 14 over the entire low frequency television band by the use of the impedance matching network comprising cartridges 33, 39 and 40. Fig. 14 of the drawings illustrates threetypical curves of voltage standing wave ratio that may be obtained in the low frequency television band. Curve D represents the standing wave ratio obtained with an impedance matching network where the antenna 10 has been substantially perfectly matched to the transmission line 12 for one particular channel in this band of frequency 1, thus giving a one-toone standing wave ratio. By modifying the values and relationship of the electrical components of the matching network comprising the cartridges 38, 39 and 453*, it is possible to obtain the curve B, which illustrates a better match for frequencies deviating substantially from frequency but obtained at a sacrifice in the voltage standing wave ratio at frequency 1. Curve F represents a further modification of the matching network comprising the cartridges 38, 39 and 40, which gives a better match for frequencies deviating from the frequency f and actually a consistent impedance match throughout the entire low frequency television band, but at a still greater sacrifice in the voltage wave ratio at frequency f.

The compromise impedance matching network and its corresponding compromise performance shown by curve F can be realized simply by replacing the shunt cartridge 40 having the reactance characteristic illustrated in Fig. 12 by another shunt cartridge 4d shown schematically in Fig. 16, having the reactance characteristic iliustrated by the curve G of Fig. 15. The curve G is discontinuous and becomes infinite near the middle of the low frequency television band and has a zero value both at zero frequency and at a frequency between the low and the high frequency television bands. When the impedance matching network contains this alternate shunt cartridge having the characteristics of Fig. 15 and the particular set of series cartridges heretofore described that are ideal for the middle frequencies of the low frequency television hand, then the broad band compromise performance over the low frequency television band and excellent performance over the high and ultra high frequency television bands is obtained. The schematic circuit diagram of Fig. 16 indicates generally the electrical component network of the compromise shunt cartridge 40. tit will be understood that the circuit shown is merely one of many that are capable of producing the reactance characteristics shown in Fig. 15 of the drawings. The electrical circuit illustrated in Fig. 16, however, is comprised of two coupled coils 6t and 61, one of which is resonated by means of a capacitor 62.

In view fo the foregoing, it will be evident that the present invention provides a television antenna which is adapted for indoor installation wherein each antenna dipole element is approximately one wave length in the middle of the ultra high frequency television band, slightly longer than a quarter wave length in the upper portion of the high frequency television band, and substantially less than a quarter wave length in the middle of the low frequency television band. it likewise provides an impedance matching network comprised of replaceable electrical component cartridges adapted to match the resultant antenna impedance to a standard transmission line impedance either for one station inthe low frequency television bands and all stations in the high and ultra high frequency television bands, or approximately matched for all stations in the low and well matched for all stations in the high and ultra high frequency television bands. Regardless of the preadjusted performance above, the antenna has a considerably narrower beam width and resultingly higher gain than a half wave length dipole in the ultra high frequency television band, yet also provides good impedance matches to signals in the low and high frequency bands. The present invention further provides a pair of hollow tubes which are adapted to serve both as a parallel conductor transmission line and as a short mast for the antenna. And also, it provides improved strain reiief means for a lead-in two-wire transmission line. Furthermore, the antenna may readily be oriented for best reception Without producing detuning of the antenna and may be used without the necessity of manually tuning the antenna when changing from one station to another.

While there have been described what are at present considered to be the preferred embodiments of the present invention, it will be understood that various changes and modifications will occur to those skilled in the art. It is aimed in the appended claims to cover all such changes and modifications which fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be Letters Patent of the United States is:

1. An indoor television antenna comprising a base of secured by insulating material, a conducting support adapted to serve as a transmission line mounted on said base, a dipole support including an insulated housing mounted on said upright support, a plate enclosed within said housing, a pair of brackets mounted on said plate, each bracket including a slotted ear protruding from said housing, an impedance matching network enclosed within said housing, means for electrically connecting said impedance matching network to said conducting support, dipole antenna elements mounted on said conducting support, said elements having means defining recesses to receive therein said slotted ears, a fastener extending through said last mentioned means and the slots in said ears to secure said dipole elements to said brackets, and means for electrically connecting said impedance matching network and said dipole antenna elements.

2. An indoor television antenna comprising a dipole support including an insulated housing, an antenna having a pair of terminals and supported by said housing, a first network matching cartridge including a parallel connected inductor and capacitor, a second network matching cartridge including a pmallel connected inductor and capacitor, and a third network matching cartridge including a parallel connected inductor and capacitor, means includingclips on said housing for interchangeably mounting said first cartridge in series with one of said terminals, means including clips on said housing for interchangeabiy mounting said second cartridge in series with the other ofsaid terminals, means for connecting a transmission line to said first and second network matching cartridges so as to connect said pair of terminals to said transmission line through said first and second network matching cartridges, means including clips on said hous- 12 ing for interchangeably mounting saidthird cartridge across said last-mentioned means, and a capacitor connected across said pair of terminals.

References Cited in the file of this patent UNITED STATES PATENTS 962,063 Swan June 2, 1910 1,065,190 Tobin June 17, 1913 1,593,738 Winning July 27,1926 1,905,276 Erickson Apr. 25, 1933 2,495,280 OBrien et a1. Jan. 24, 1950 2,531,035 Epstein Nov. 21, 1950 2,542,884 Trebules Feb. 20, 1951 2,545,681 Zepp Mar. 20, 1951 2,558,487 Hills June 26, 1951 2,563,243 Hills Aug. 7, 1951 2,569,810 Hamel et a1 Oct. 2, 1951 2,615,005 White Oct. 21, 1952 2,644,888 Root July 7, 1953 .2,657,3 62 Epperson Oct. 27, 1953 2,666,138 Ehrbar June 12, 1954 2,671,201 Williams Mar. 2, 1954 2,754,490 Schnoll July 10, 1956 OTHER REFERENCES Pub. Development of Fan Type'TV Ante'nnaj Radio and Television News, May 1950, pp. 66, 67, 132.

Pub. 111: UHF Antennas, Radio and Television News, Feb. 1953, pp. 56, 57, 58. 1

Article: New Approach to Conical Antenna Design, by Wade Radio and Television News, May 1954 (page 76 relied on). 

